In the production of multilayered printed circuit boards holes are formed in said boards to generate contact between the single layers, which holes are then filled with a conductive material or which, for the purpose of saving such a material, are coated for example only on their peripheral walls with metal, and are then closed with a more cost-effective material, such as epoxy resin.
The holes are closed in order to minimize the total surface of the printed circuit board. In addition, for example soldering base pads can be provided on a refilled hole for component parts, such as transistors, ICs, etc. which are to be connected to the printed circuit board. Moreover, a hole in an intermediate layer of the printed circuit board can be used to provide an electrical connection of both sides of said intermediate layer. After filling the hole, the same surface can be used again for a smaller borehole in order to generate, for example, a contact connection between printed circuit board layers which are located more outside.
In this context, for example air bubble and/or foreign particle inclusions may occur when the holes are filled with the filling material, which reduces the quality of the filling and thus the quality of the board.